Stap-specifieke sorteren van Muis Spermatiden door flowcytometrie
Summary
We describe a sorting strategy for mouse spermatids using flow cytometry. Spermatids are sorted into four highly pure populations, including round (spermiogenesis steps 1-9), early elongating (spermiogenesis steps 10-12), late elongating (spermiogenesis steps 13-14) and elongated spermatids (spermiogenesis steps 15-16). DNA staining, size and granulosity are used as selection parameters.
Abstract
De differentiatie van muis spermatiden is een kritisch proces voor de productie van een functionele mannelijke gameet een intact genoom aan de volgende generatie over te dragen. Tot nu toe zijn moleculaire studies van deze morfologische overgang belemmerd door het ontbreken van een methode waarmee een goede scheiding van deze belangrijke stappen spermatide differentiatie voor latere analyses. Eerdere pogingen tot goede gating van deze cellen via flowcytometrie kan moeilijk zijn omdat een bijzondere toename DNA fluorescentie in spermatiden ondergaan chromatine hermodellering. Op basis van deze waarneming, geven we gegevens van een eenvoudige flowcytometrie regeling, waardoor reproduceerbare zuivering van vier populaties van muis met ethanol vaste spermatiden, die elk een andere toestand in het vernieuwingsproces kern. Bevolking verrijking wordt bevestigd met behulp van stap-specifieke merkers en morfologische criteria. Het gezuiverde spermatiden kan worden gebruikt voor genomische en proteomic analyses.
Introduction
Haploid round spermatids differentiate into spermatozoa by a process called spermiogenesis. This involves many different steps including the acquisition of a flagellum, chromatin and cytoskeleton remodeling, condensation of the nucleus as well as the loss of most of the cytoplasm. These unique cellular events must be finely regulated in order to produce a mature functional gamete with an intact genome suitable for fertilization. Spermiogenesis can hardly be studied in vitro since no reliable cell culture system has so far been able to support progression through the different steps of the process. Moreover, actual in vitro techniques lead to a poor yield1,2. In vivo, proper transitions through the different steps of spermiogenesis are crucial for the natural functional integrity of the male gamete. Successful purification of spermatids according to their differentiation steps has never been accomplished with a level of enrichment sufficient to allow molecular characterization of spermiogenesis. For instance, purification of key steps of the spermatidal differentiation would be especially useful to study the developing acrosome, formation of the midpiece3, cell junction dynamics4, RNA dynamics5, chromatin remodeling process6,7 or genomic stability8. Purification of spermatids has been hampered by their progressive morphological transformation, the lack of known stage-specific external biomarkers, and their peculiar shape and size.
Although most male germ cells display a direct relationship between DNA staining and ploidy (DNA content), we noticed that such positive correlation is no longer applicable to spermatids. This stems from our early observation that seminiferous tubule sections show variable intensity of DNA staining throughout the different spermiogenesis steps. Although DNA staining is consistent with their haploid set of chromosomes from spermiogenesis steps 1 to 7 (round spermatids), we observed a sharp increase in fluorescence intensity with DAPI or SYTO 16 around the onset of nuclear reorganization and chromatin remodeling (spermiogenesis step 8) reaching a peak at the onset of nuclear condensation (spermiogenesis steps 11-12). Following condensation of the nucleus, DNA staining intensity decreases until spermiation (spermiogenesis step 16). We surmised that this was likely associated with the formation of their peculiar chromatin structure transition where histones are replaced by protamines. We therefore developed a reliable flow cytometry method that allows the separation of spermatids using the variation of DNA intensity of spermatids as a main selection parameter.
A simple flow cytometry approach is described to separate mouse spermatids with high purity (95-100%) based on their apparent DNA content (SYTO16 staining), size and granulosity. Spermatids are separated into four populations; spermiogenesis steps 1-9, 10-12, 13-14 and 15-16. Purified spermatids are suitable for genetic/genomic analysis, as well as proteomic applications as described in a recent publication from our group9.
Protocol
Representative Results
Discussion
Spermatogenese cellen altijd uitdagend om te studeren gezien de complexiteit van de seminiferus epitheel, en het beperkte succes van in vitro kweek. In de loop der jaren vele benaderingen zuiveren kiemcellen van verschillende species ontwikkeld. Sedimentatie technieken met behulp van de zwaartekracht zuiveren met Percoll of runderserumalbumine hellingen bieden meestal een goede opbrengst van intacte kiemcellen, maar gebrek aan een goede definitie tussen sommige celtypen, zoals de meiose tetraploïde cellen en s…
Declarações
The authors have nothing to disclose.
Acknowledgements
De auteurs willen dr Leonid Volkov en Éric Bouchard bedanken voor hun technisch advies over epifluorescentiemicroscopie.
Financiële steun
Gefinancierd door de Canadian Institutes of Health Research (subsidie # MOP-93781) naar GB
Materials
| Isoflurane | ABBOT | 05260-05 | For mouse anesthesia before euthanasia |
| Fetal bovine serum | Wisent | 90150 | For tube coating |
| 1X PBS | |||
| EDTA | BioShop | EDT | For sorting buffer preparation |
| HEPES | Sigma | H | For sorting buffer preparation |
| 100 % Ethanol | Les alcools de commerce | 092-09-11N | For cell fixation |
| SYTO 16 | Life Technologies | S7578 | DNA staining |
| 5 ml polypropylene round bottom tubes | BD Falcon | 352063 | Sorted cells collection |
| 15 ml polypropylene conical bottom tubes | PROgene | 1500 | |
| 50 ml polypropylene conical bottom tubes | PROgene | 5000 | |
| TEC4 anaesthetic vaporizer | Ohmeda | 1160526 | For mouse euthanasia |
| CO2 gas tank | Praxair | C799117902 | For mouse euthanasia |
| O2 gas tank | Praxair | O254130501 | For mouse euthanasia |
| Homemade mouse gas chamber | For mouse euthanasia | ||
| 40 µm Falcon cell strainer | Corning Incorporated | 352340 | |
| 50-micron sample line filters | BD Biosciences | 649049 | |
| Vortex mixer | Labnet international, inc. | S0200 | For cell fixation |
| Dynac centrifuge | Clay Adams | 101 | |
| Celltrics 50 µm filters | Partec | 04-004-2327 | |
| 488 nm laser-euipped cell sorter | BD Biosciences | FACSAria III | |
| Accudop Fluorescent Beads | BD Biosciences | 345249 | |
| Sorting Buffer: 1X PBS, 1mM EDTA pH 8.0, 25mM HEPES pH 7.0, 1%FBS | FBS is heat-inactivated. Make fresh solution, 0.22 μm filtered and keep at 4°C. |
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